While I tend to agree with rainbow's last post, I have had a FO ask me if it was ok to listen to his iPod on a long night flight, and I simply told himit was ok, as long as he didn't miss any calls by ATC. He missed no more than the rest of us tend to do, and I was fine with it. Another guy would ask if it is ok to read the paper or whatever, and that is just as fine, as long as general vigilance is not impaired too much.
Everyone has their own way of survivng the long nights awake, be it looking at stars or reading or whatever.
For me music doesn't work too well, even though an occasional well chosen song someone played on 123.45 on the Atlantic was quite romantic.
Nic